I. Field of the Invention
The invention concerns an aircraft braking method and a ducted fan jet engine for implementing the method.
II. Description of Related Art
In civil aviation, the jet engines used are generally so-called ducted fan jet engines. From downstream to upstream, in the direction of the gas stream, they comprise a fan, one or more compressor stages, a combustion chamber, one or more turbine stages and an exhaust nozzle. Part of the air stream driven by the fan, called primary flow or hot flow, is driven towards those parts of the jet engine core listed above. The remainder of the air stream, called secondary flow or cold flow, is directly ejected at the outlet of the fan into a secondary exhaust nozzle located between the outer case of the jet engine core and the engine nacelle. Part of the secondary flow may possibly be re-injected into the primary flow for cooling purposes for example, but the major part of this secondary flow is only used to obtain jet engine thrust. With ducted fan jet engines for civil use, the turbofan thrust is mainly derived from the secondary flow.
At the rear part of their nacelle, jet engines have thrust reversers used during the landing phase to cause thrust in the opposite direction to the aircraft's motion and to facilitate its braking. Thrust reversers are in the form of flaps possibly arranged radially in the secondary flow and oriented, outwardly, towards upstream of the jet engine in order to cause the encountered air stream to move towards upstream of the jet engine, thereby reversing the thrust produced.
On aircraft landing, firstly the power of the jet engine is reduced to enable the aircraft to touch down, then the thrust reversers are set in operation and engine power is subsequently increased to increase the counter-thrust produced by the reversers.
These thrust reversing devices used for braking an aircraft have disadvantages. Firstly they are heavy and complex, which is all the more detrimental when positioned at the rear of the jet engine, creating an overhang with respect to the engine mounting plane on the wing of the aircraft. In addition, reduction in engine power followed by increased throttling lead to high fuel consumption on landing. Mechanical stresses on the jet engine parts at the time of thrust reversion are high. The fan in particular has its lifetime reduced on account of operations using thrust reversers. Finally, landing procedure is relatively complex with the succession of engine power reductions and increases.
The present invention sets out to overcome these disadvantages.